Part of Brighton Marina had to be evacuated after part of a World War II torpedo was discovered.
Police officers and Royal Navy bomb disposal experts were called to the scene at about 1920 BST on Saturday after reports of a mine tied to a jetty.
A number of buildings at the marina were evacuated for several hours while the situation was dealt with.
The navy experts found the mine was part of a wartime torpedo which did not actually contain any explosives.
It is thought the object was found off the Brighton coast by a diver who towed it into the marina and tied it to the jetty.
Homes and businesses in the immediate vicinity of where it was found were emptied amid fears it could explode.
Police said it was about three hours before the Royal Navy had arrived at the scene and established the torpedo section was safe.